The drilling type sidewall coring apparatus is a petroleum exploration apparatus. US patent US 2013/0068531A1 discloses a drilling type sidewall coring apparatus. As shown in FIG. 1, a coring apparatus 100 is lowered into a well, a bit 1002 drills into the formation, perpendicular to the sidewall, for coring and core folding operations, and the bit 1002 completes the core-pushing operation after retracting into a main body 1001. The operation process of the coring apparatus 100 is: a ground panel controls an electric motor of the downhole coring apparatus 100, the electric motor drives a hydraulic pump to produce high pressure to drive a backup arm 1003 to deploy such that the coring apparatus is fixed in the depth of coring and is pressed firmly against the sidewall; meanwhile, the high pressure produced by the hydraulic system drives a hydraulic motor, the hydraulic motor drives the diamond bit to screw into the formation; after drilling to the target length, the rock core of the formation is obtained by the action of core folding.
The bit of the above coring apparatus is mounted on the hydraulic motor and the power transmission line of driving the bit is: electric motor→hydraulic pump→hydraulic motor→bit. However, the power transmission efficiency of hydraulic pump and hydraulic motor is very low, particularly when the temperature is of great changes, the viscosity of hydraulic oil varies a lot, even the efficiency is lower. Thus, the effective power transmitted from the electric motor to the bit 1002 is very small, about 20%. In order to guarantee the bit 1002 to have sufficient power to complete coring operation, the power of the electric motor must be very large, while the request for large power of the electric motor leads to the great difficulty of downhole power supply and higher risk. In addition, because the viscosity of hydraulic oil is mainly affected by the temperature, and the power transmission efficiency of hydraulic system is closely related with viscosity, the range of operating temperature of the instrument with one same hydraulic oil is narrower and it needs to frequently replace different hydraulic oil according to the different downhole operating temperature to complete coring operation.
The bit 1002 of the above coring apparatus needs to protrude to press firmly against the sidewall relative to the main body 1001 when drilling and the bit 1002 needs to be retracted into the main body 1001 after core folding. The mechanism for achieving protruding and retracting of the bit of the above coring apparatus comprises a first hydraulic oil cylinder mounted on the main body 1001, a long motion guide rail and a short motion guide rail; the protruding or retracting of the bit 1002 relative to the main body 1001 can be achieved relying on the drive of the first hydraulic oil cylinder and the cooperative movement of a sliding block mounted on the hydraulic motor with the long motion guide rail and short motion guide rail. Such achievement depends on the design of the track and the request for manufacturing precision of the apparatus is higher.
The bit 1002 of the above coring apparatus needs to be rotated to make the bit 1002 rotate to the core pushing position (at this time, the axial direction of the bit is parallel to the axial direction of the main body) to complete core pushing operation, or rotate the bit 1002 to the initial position (at this time, the axial direction of the bit is perpendicular to the axial direction of the main body). The above coring apparatus needs to drive the bit to swing at the coring position to complete core folding operation. The above coring apparatus drives the hydraulic motor by a piston of a second hydraulic oil cylinder and a linkage mechanism and is cooperatively moved with the long motion guide rail and short motion guide rail relying on the sliding block mounted on the hydraulic motor to achieve the rotation and swing of the bit 1002. Since the achievement depends on the design of the track, the request for manufacturing precision of the apparatus is higher. Besides, because when the bit 1002 protrudes and retracts, the position of the second hydraulic oil cylinder and the linkage mechanism relative to the hydraulic motor is varying, thus the core folding operation can be completed only when the coring depth of the bit 1002 is sufficiently deep. If the bit 1002 gets stuck to not reach the appointed depth during the coring process, the core folding and coring cannot be achieved.